Triggers of tree mortality under drought conditions

This is a gene-environment interactions topic. The “environmental signal” in this case is DROUGHT. Which genes in the tree’s genome will respond to the drought signal in order for the tree to survive? Forests provide a wide array of ecosystem services and are vital for maintenance of biodiversity. Whereas forests continue to face pressure from expanding human populations –– which lead to changes in land use and deforestation –– the threat posed by harsh changes in weather is less easily quantified. Evidence from a wide range of sources suggests that rising atmospheric CO2 concentrations have benefited forests, with CO2 fertilization enabling an increased leaf-area index, enhanced water-use efficiency, and greater uptake of carbon globally.

However, extreme weather events, such as heat waves, droughts, fires and storms, have the potential to offset these benefits –– causing widespread tree mortality and a net loss of CO2 into the atmosphere. Although forests are vulnerable to a wide range of extreme weather events, drought and associated disturbances have the greatest effect globally. In the [attached] Review, authors examine the physiological response of trees to drought, focusing on new insights provided by rapid advances in our understanding of the hydraulic function of plants.

Land plants require an efficient long-distance transport pathway to lift water from the soil to their leaves at a rate that satisfies transpiration.

In trees, the xylem tissue (wood) supplies water for all aspects of plant function, including photosynthesis, growth and reproduction. During long droughts, damage to this hydraulic supply network as a consequence of severe water stress has been identified as a key mechanism involved in tree mortality. Recent experimental work has quantitatively linked hydraulic-failure thresholds to plant mortality, and field studies have shown that hydraulic failure is a primary pathway for extensive canopy death or plant mortality during natural drought events. Authors herein focus on the current understanding of tree hydraulic performance under drought conditions, how to identify physiological thresholds that precipitate mortality, and the mechanisms of recovery after the drought is over.